X-ray radiography imaging of cargo containers and trucks for the detection of Special Nuclear Material (SNM) and other contraband requires high-intensity X-ray radiation sources. The higher the intensity at a specific source energy, the greater the amount of material the X-ray beam can penetrate, and the better the resulting contrast and resolution. In conventional practice, the X-ray source intensity of an inspection system is set to the highest level allowable under the particular circumstances of the system and the inspection area, referred to as the Output Set Point (OSP) of the source, and all cargo is inspected using this fixed intensity, whether an accurate inspection of the cargo requires this intensity or not. This OSP is typically not the highest rated intensity that the source is capable of producing. More often than not, the OSP is set so that the source does not exceed a predetermined specified radiation dose limit at the boundary of a predefined exclusion zone, or, in the case of a portal inspection system (where truck drivers drive their trucks through the inspection system), to stay below a certain dose limit to the driver of the inspected truck.
While conventional inspection systems are capable of providing higher cargo penetration, they are inefficient in that they do not take advantage of the rated maximum intensity of the source, which is usually higher than the OSP. In addition, conventional inspection systems use much higher intensity than needed for certain cargos (or portions thereof), leading, on average, to unnecessarily high radiation levels around the inspection system.
What is needed therefore is an inspection system and method of using such inspection system that has the capability of delivering the minimum X-ray intensity needed to sufficiently image and/or penetrate cargo.
What is also needed is a mobile or truck mounted inspection system and method that is capable of using an intensity-modulated 6 MeV or higher X-ray source with consideration for weight-bearing and shielding requirements.